This project will examine the operation of attention at two coarsely defined stages of processing, namely visual perception and visual working memory. Most theories of attention do not accommodate the possibility that attention might have different properties in different cognitive subsystems, and the goal of this project will be to demonstrate that there are actually several differences between the attentional mechanisms that operate during perception and those that operate during working memory. For example, we will test the hypothesis that the highly spatiotopic organization of visual perception is mirrored by perceptual- level attentional mechanisms with spatiotopic properties, such as a broad spatial gradient and an inability to focus attention on two separate locations without attending to the intervening region. This contrasts with the more abstract nature of object representations in working memory, which we expect to be mirrored by attentional mechanisms that will lack the spatiotopic properties of perceptual-level attention and instead be object-based. To examine the properties of perceptual-level and working memory-level attention, we will use a combination of behavioral/psychophysical methods and electrophysiological recordings (specifically event-related potentials). In particular, we will compare "memory-intensive" tasks in which working memory is overloaded but the perceptual demands are minimal with "perception-intensive" tasks in which memory is not overloaded but the perceptual demands are great. Attention should operate at different stages in these tasks, allowing us to isolate the properties of perceptual-level and working memory-level attentional mechanisms. This program of research will have important long-term implications for psychological/psychiatric disorders in which attention is compromised, such as attention deficit disorder, reading disorders, and schizophrenia. Specifically, by developing methods to isolate specific attentional mechanisms and by assessing the characteristics of each attentional mechanism, it will be easier to identify the specific attentional mechanisms that are compromised in a given disorder and to understand how the attentional impairments impact the overall disorder.